This invention relates to a rotary lawnmower using a horizontal blade and to a device to couple to rotory blade to the engine only when an operator is present, and to automatically decouple the rotory blade from the engine drive shaft whenever the lawnmower is left unattended with the engine running.
Automatic stop or "deadman" devices have been used in applications where there is a need for continuous operator control of a dangerous instrumentality. The most typical example is with a train locomotive. If the engineer releases his grasp on a control lever, the deadman's device operates both to interrupt drive power from the locomotive's engines and to brake the train to a halt.
In the field of lawnmowers, there is a recognized need for interrupting power to the lawnmower's blades when the operator releases his grasp upon the lawnmower's handle. For instance, the lawnmower operator may wish to clear accumulated grass from under the grass containment hood of the lawnmower. Doing so with the blades continuing to rotate under power is dangerous.
Likewise, an operator of a lawnmower will sometimes have to temporarily leave his lawnmower to do some other errand. However, he may not turn the lawnmower's motor off. But unless he does, the lawnmower operating with its blades rotating under power represents a hazard to children.
A deadman device acts to ameliorate this problem by automatically disrupting power to the blades when the operator releases his grasp of the lawnmower's handle.
The most common automatic shut down device used today is a hand held switch which must be depressed by the operator to keep the engine spark plug from being shorted out. This means that the engine must be restarted even when the operator accidentally releases his grip on the handle switch. Such devices are easily and usually disabled by lawnmower users as soon as they buy the machine.
While other deadman devices have previously included disengageable clutch means, no prior art lawnmower deadman device known to applicant has included magnetically coupled disengageable blade drive means.
A constant hazard in the use of horizontal rotary blade lawnmowers is the damage done by the blade striking stones or other solid objects on the lawn. In addition to this obvious danger of thowing the stone to cause injury or damage to people, animals and/or property hereby; there is often severe damage to the blade and even the motor crankshaft to which the blade has heretofore been rigidly attached.
An example of a structure in which an electromagnetic winding is used to activate a clutch between a drive member and a driven member is shown in the Miller patent, U.S. Pat. No. 3,677,377, issued in July of 1972. This structure does not embody the fail-safe use of gravity to decouple the driven member from the drive member, and does not anticipate the inventive concept of the present invention.
Another example of a magnetic clutching device is seen in the patent of Thomas, U.S. Pat. No. 2,479,986, issued in August of 1949.
A constant and unchangeable friction pressure to couple a lawnmower blade to a drive shaft is shown in the patent of Thelander, U.S. Pat. No. 2,707,362.
The patent to Havercamp et al, U.S. Pat. No. 3,570,226, utilizes the electromagnetic force of the electric lawnmower drive motor to hold a disc brake plate away from a brake lining while the electric lawnmower drive motor is actually rotating. This structure would not be useful to disconnect a lawnmower rotor blade from a lawnmower while the motor was still running.
A search was made prior to the filling of this application, and the above patents as well as the patents listed below aare cited by the searcher. The patents set out below are not believed to be particularly pertinent to the invention:
U.S. Pat. No. 1,012,521 to Coldwell, granted in December of 1911;
U.S. Pat. No. 2,259,824 to Lowder, granted in October of 1941;
U.S. Pat. No. 2,571,762 to Rich et al, granted in October of 1951;
U.S. Pat. No. 3,240,304 to Wickersham; granted in March of 1966;
U.S. Pat. No. 3,417,271 to Reed, granted in December of 1968; and
U.S. Pat. No. 3,774,379 to Mizobata et al, granted in November of 1973.
Neither the inventor nor those in privity with him know of any prior art which is closer than that listed and discussed above. They know of no prior art which anticipates the claims presented herein.
In order to overcome the difficulties discussed above and other difficulties, the structure of the present invention was developed.